LOOP-IN SYSTEMS
Loop-in lighting wiring is the modern cabling arrangements used in most installation. Generally it uses less materials and is quicker to install than radial (junction box) wiring - it can however, be a bit more complicated to work out the actual wires at a ceiling rose.
This page shows the various wirings found at a ceiling rose of an installation using loop-in lighting wiring.
Note that the colours shown connected to the ceiling rose are the old standard - red, black and yellow and green.
The modern standard being brown, blue and yellow and green (the yellow and green being the earth connector which is typically uninsulated but fitted with a yellow and green sleeving.)
Unlike radial lighting wiring, loop-in wiring is more complicated at the ceiling rose:
1 Common loop-in wiring
1A - This is the most common loop-in wiring arrangement you are likely to see. It shows three cables; one cable (L+N+E) either from the mains board or the last ceiling rose, one cable (L+N+E) out to the next ceiling rose, and one cable (L+S/L +E) that goes to the wall or pull switch within that room. The latter cable is referred to as the switch live (S/L) provides electric to the light when the switch is turned on.
 Fig 1A |
 Fig 1B |
If you have to disconnect and remove the cores from the ceiling rose reconnect them as shown in 1B.
If the light fitting you have purchased has just two cores - live (brown) and neutral (blue), connect the live to the switch live terminal and neutral to the neutral terminal. If the fitting has an earth core, it must be sleeved with a yellow and green coat and connected to the Earth terminal.
Important: Where Earth cores are present, they must ALL be connected together in the same terminal.
2 Wiring for end of loop
2A - This wiring arrangement would indicate that this is an end of the loop light fitting. It has one less live, one less neutral and one less earth core because the loop-in has reached the end and doesn't need to pass power on to another ceiling rose.
 Fig 2A |
 Fig 2B |
If you have to disconnect and remove the cores from the ceiling rose reconnect them as shown in 2B.
If the light fitting you have purchased has two cores - live (brown) and neutral (blue) connect the live to the switch live terminal and neutral to the neutral terminal. If the fitting has an earth core, it must be sleeved with a yellow and green coat and connected to the Earth terminal.
Important: Where Earth cores are present, they must ALL be connected together in the same terminal.
3 Wiring for two lights on one light switch
3A - This wiring arrangement would indicate the presence of two lights in a room on the same light switch. If there were one less red (live),one less black (neutral) and one less yellow/green (earth), this would indicate that this is the end of the loop.
 Fig 3A |
 Fig 3B |
If you have to disconnect and remove the cores from the ceiling rose reconnect them as shown in 3B.
If the light fitting you have purchased has two cores - live (brown) and neutral (blue) connect the live to the switch live terminal and neutral to the neutral terminal. If the fitting has an earth core, it must be sleeved with a yellow and green coat and connected to the Earth terminal.
Important: Where Earth cores are present, they must ALL be connected together in the same terminal.
4 Lighting with connected extractor fan
A - This wiring arrangement would most frequently be found in a bathroom, or kitchen that has an extractor fan with a run-on timer. If this was at the end of the loop, it would have one less red (live), one less black core (neutral), and one less yellow/green (earth).
 Fig 4A |
 Fig 4B |
If you have to disconnect and remove the cores from the ceiling rose reconnect them as shown in 4B.
If the light fitting you have purchased has two cores - live (brown) and neutral (blue) connect the live to the switch live terminal and neutral to the neutral terminal. If the fitting has an Earth core, it must be sleeved with a yellow and green coat and connected to the Earth terminal.
Important: Where Earth cores are present, they must ALL be connected together in the same terminal.
(originally on, and copyright of, userview.net)